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Q & A: How you determine the order of magnitude of the mass of the earth?

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Most recent answer: 02/23/2015
Q:
How you determine the order of magmitude of the mass of the earth?
- Dorcas (age 15)
Port Moresby,Papua New Guinea
A:

Hi Dorcas,

You know that the gravitational force between the earth and and arbitrary object is F = Me m G / Re 2 where G is the gravitational constant 6.6710-11 Nm2/kg2, Re = 6.4*106 m, and m is the mass of the object.   You also know that the force on the object is F = mg where g = 9.8 m/s2  is the acceleration of an object due to the earth's gravity.   Solving for Me you get  Me = Re 2 g/G = 6*1024 kgm.

LeeH

And you may wonder, where did the value for G come from? Cavendish got it by measuring the gravitational force betwen two known masses.  /mw

 

 


(published on 02/23/2015)

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